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Magnetic field effects

Kangkang Meng, Jun Miao, Xiaoguang Xu, Yong Wu, Jiaxing Xiao, Jianhua Zhao, Yong Jiang
We report modulated switching current density and spin-orbit torques (SOT) in MnGa/Ta films with inserting very thin Co2FeAl and Co layers. Ferromagnetic coupling has been found in MnGa/Co2FeAl/Ta, resulting in a decreased effective anisotropy field. On the contrary, in MnGa/Co/Ta, antiferromagnetic coupling plays a dominant role. The switching current density Jc in MnGa/Ta is 8.5 × 10(7) A/cm(2). After inserting 0.8-nm-thick Co2FeAl and Co, theJc becomes 5 × 10(7) A/cm(2) and 9 × 10(7) A/cm(2), respectively...
December 2, 2016: Scientific Reports
Simon Gross, Christoph Barmet, Benjamin E Dietrich, David O Brunner, Thomas Schmid, Klaas P Pruessmann
High-field magnets of up to tens of teslas in strength advance applications in physics, chemistry and the life sciences. However, progress in generating such high fields has not been matched by corresponding advances in magnetic field measurement. Based mostly on nuclear magnetic resonance, dynamic high-field magnetometry is currently limited to resolutions in the nanotesla range. Here we report a concerted approach involving tailored materials, magnetostatics and detection electronics to enhance the resolution of nuclear magnetic resonance sensing by three orders of magnitude...
December 2, 2016: Nature Communications
J Ko
The sensitivity of the pitch angle profiles measured by the motional Stark effect (MSE) diagnostic to the evolution of the safety factor, q, profiles during the tokamak sawtooth events has been investigated for Korea Superconducting Tokamak Advanced Research (KSTAR). An analytic relation between the tokamak pitch angle, γ, and q estimates that Δγ ∼ 0.1° is required for detecting Δq ∼ 0.05 near the magnetic axis (not at the magnetic axis, though). The pitch angle becomes less sensitive to the same Δq for the middle and outer regions of the plasma (Δγ ∼ 0...
November 2016: Review of Scientific Instruments
P D VanMeter, P Franz, L M Reusch, J S Sarff, D J Den Hartog
The Soft X-Ray (SXR) tomography system on the Madison Symmetric Torus uses four cameras to determine the emissivity structure of the plasma. This structure should directly correspond to the structure of the magnetic field; however, there is an apparent phase difference between the emissivity reconstructions and magnetic field reconstructions when using a cylindrical approximation. The difference between the phase of the dominant rotating helical mode of the magnetic field and the motion of the brightest line of sight for each SXR camera is dependent on both the camera viewing angle and the plasma conditions...
November 2016: Review of Scientific Instruments
X H Yin, Y Y Li, J Fu, D Jiang, S Y Feng, Y Q Gu, Y Cheng, B Lyu, Y J Shi, M Y Ye, B N Wan
A Charge eXchange Recombination Spectroscopy (CXRS) diagnostic system has been developed to measure profiles of ion temperature and rotation since 2014 on EAST. Several techniques have been developed to improve the spatial calibration of the CXRS diagnostic. The sightline location was obtained by measuring the coordinates of three points on each sightline using an articulated flexible coordinate measuring arm when the vessel was accessible. After vacuum pumping, the effect of pressure change in the vacuum vessel was evaluated by observing the movement of the light spot from back-illuminated sightlines on the first wall using the newly developed articulated inspection arm...
November 2016: Review of Scientific Instruments
Wenzhe Mao, Peng Yuan, Jian Zheng, Weixing Ding, Hong Li, Tao Lan, Adi Liu, Wandong Liu, Jinlin Xie
A compact and lightweight support platform has been used as a holder for the interferometer system on the Keda Torus eXperiment (KTX), which is a reversed field pinch device. The vibration caused by the interaction between the time-varying magnetic field and the induced current driven in the metal optical components has been measured and, following comparison with the mechanical vibration of the KTX device and the refraction effect of the ambient turbulent air flow, has been identified as the primary vibration source in this case...
November 2016: Review of Scientific Instruments
C Ruiz, S T A Kumar, F S B Anderson, D T Anderson
The effect of variation in atomic level population of a neutral beam on the Motional Stark Effect (MSE) measurements is investigated in the low density plasmas of HSX stellarator. A 30 KeV, 4 A, 3 ms hydrogen diagnostic neutral beam is injected into HSX plasmas of line averaged electron density ranging from 2 to 4 ⋅ 10(18) m(-3) at a magnetic field of 1 T. For this density range, the excited level population of the hydrogen neutral beam is expected to undergo variations. Doppler shifted and Stark split Hα and Hβ emissions from the beam are simultaneously measured using two cross-calibrated spectrometers...
November 2016: Review of Scientific Instruments
T Ino, H Hayashida, H Kira, T Oku, K Sakai
Spin polarized (3)He gas is currently widely used in various scientific fields and in medical diagnosis applications. The spin polarization of (3)He nuclei can be achieved by spin-exchange optical pumping (SEOP). In SEOP, the (3)He gas is enclosed in a glass cell together with alkali metals and is then heated to maintain the alkali metal vapor pressures at the appropriate levels. However, polarized (3)He gas is highly sensitive to any inhomogeneity in its magnetic field, and any small field gradients caused by the heaters may cause degradation of the (3)He polarization...
November 2016: Review of Scientific Instruments
Zichao Li, Hong Li, Cui Tu, Jintong Hu, Wei You, Bing Luo, Mingsheng Tan, Yolbarsop Adil, Yanqi Wu, Biao Shen, Bingjia Xiao, Ping Zhang, Wenzhe Mao, Hai Wang, Xiaohui Wen, Haiyang Zhou, Jinlin Xie, Tao Lan, Adi Liu, Weixing Ding, Chijin Xiao, Wandong Liu
In a reversed field pinch device, the conductive shell is placed as close as possible to the plasma so as to balance the plasma during discharge. Plasma instabilities such as the resistive wall mode and certain tearing modes, which restrain the plasma high parameter operation, respond closely with conditions in the wall, in essence the eddy current present. Also, the effect of eddy currents induced by the external coils cannot be ignored when active control is applied to control instabilities. One diagnostic tool, an eddy current probe array, detects the eddy current in the composite shell...
November 2016: Review of Scientific Instruments
Alexander Pikin, James G Alessi, Edward N Beebe, Deepak Raparia, John Ritter
Electron diode guns, which have strongly varying magnetic or electric fields in a cathode-anode gap, were investigated in order to generate laminar electron beams with high current density using magnetically immersed guns. By creating a strongly varying radial electric field in a cathode-anode gap of the electron gun, it was demonstrated that the optical properties of the gun can be significantly altered, which allows the generation of a laminar, high-current electron beam with relatively low magnetic field on the cathode...
November 2016: Review of Scientific Instruments
I Ďuran, S Entler, M Kohout, M Kočan, G Vayakis
Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified. It was demonstrated that this effect can be minimized by the optimization of the sensor geometry and alignment with the magnetic field and by the application of "current-spinning technique...
November 2016: Review of Scientific Instruments
L Makinistian
A novel system of coils for testing in vitro magnetobiological effects was designed, simulated, and built. Opposite to what is usual, the system generates a controlled gradient of magnetic field. This feature is introduced to allow the assessment of multiple values of the field in a single experiment. The apparatus consists of two flattened orthogonal coils, which permit independent control of two of the spatial components of the field. Geometry of design, combined with the use of a standard multi-well microplate for cellular culture, allows for simultaneous testing of 96 different field conditions...
November 2016: Review of Scientific Instruments
L Z Zhu, Z P Chen, F M Li, H Liu, Z Y Chen, G Zhuang
Due to the existence both of toroidal ripples and toroidal field (TF) current diffusion, the toroidal flux changes with time when the TF current is at the flat-top. A diamagnetic measurement based on the compensation of TF current diffusion has been built in J-TEXT to solve this problem. The measurement system includes a double-loop installed in the vacuum vessel and an array of small printed circuit board (PCB) magnetic probes placed on the mid-plane of one TF coil. A model was proposed to analyze and compensate the effect of TF current diffusion...
November 2016: Review of Scientific Instruments
Deepak K Gupta
Hanle effect is presented as a low magnetic-field diagnostic for field-reversed configuration (FRC) plasmas. The non-perturbative technique is capable of measuring not only magnetic-field profile and direction but also field-null position and its shape. Conditions and configurations for the measurement are discussed. The technique is applicable to other low magnetic-field laboratory plasmas, e.g., magnetic-cusps, where measurements of low field are desirable, and it may also be extended to measure the two-dimensional vector magnetic-field...
November 2016: Review of Scientific Instruments
Merlin Pohlit, Paul Eibisch, Maryam Akbari, Fabrizio Porrati, Michael Huth, Jens Müller
Alongside the development of artificially created magnetic nanostructures, micro-Hall magnetometry has proven to be a versatile tool to obtain high-resolution hysteresis loop data and access dynamical properties. Here we explore the application of First Order Reversal Curves (FORC)-a technique well-established in the field of paleomagnetism for studying grain-size and interaction effects in magnetic rocks-to individual and dipolar-coupled arrays of magnetic nanostructures using micro-Hall sensors. A proof-of-principle experiment performed on a macroscopic piece of a floppy disk as a reference sample well known in the literature demonstrates that the FORC diagrams obtained by magnetic stray field measurements using home-built magnetometers are in good agreement with magnetization data obtained by a commercial vibrating sample magnetometer...
November 2016: Review of Scientific Instruments
J Chen, W X Ding, D L Brower, D Finkenthal, C Muscatello, D Taussig, R Boivin
Motivated by the need to measure fast equilibrium temporal dynamics, non-axisymmetric structures, and core magnetic fluctuations (coherent and broadband), a three-chord Faraday-effect polarimeter-interferometer system with fast time response and high phase resolution has recently been installed on the DIII-D tokamak. A novel detection scheme utilizing two probe beams and two detectors for each chord results in reduced phase noise and increased time response [δb ∼ 1G with up to 3 MHz bandwidth]. First measurement results were obtained during the recent DIII-D experimental campaign...
November 2016: Review of Scientific Instruments
E Viezzer, R Dux, M G Dunne
A new edge beam emission polarimetry diagnostic dedicated to the measurement of the magnetic field line angle has been installed on the ASDEX Upgrade tokamak. The new diagnostic relies on the motional Stark effect and is based on the simultaneous measurement of the polarization direction of the linearly polarized π (parallel to the electric field) and σ (perpendicular to the electric field) lines of the Balmer line Dα. The technical properties of the system are described. The calibration procedures are discussed and first measurements are presented...
November 2016: Review of Scientific Instruments
T Roche, M C Thompson, R Mendoza, I Allfrey, E Garate, J Romero, J Douglass
External flux conserving coils were installed onto the exterior of the C-2U [M. W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015)] confinement vessel to increase the flux confinement time of the system. The 0.5 in. stainless steel vessel wall has a skin time of ∼5 ms. The addition of the external copper coils effectively increases this time to ∼7 ms. This led to better-confined/longer-lived field-reversed configuration (FRC) plasmas. The fringing fields generated by the external coils have the side effect of rendering external field measurements invalid...
November 2016: Review of Scientific Instruments
E C Dutra, J A Koch, R Presura, W A Angermeier, T Darling, S Haque, R C Mancini, A M Covington
Spectroscopic techniques in the visible range are often used in plasma experiments to measure B-field induced Zeeman splitting, electron densities via Stark broadening, and temperatures from Doppler broadening. However, when electron densities and temperatures are sufficiently high, the broadening of the Stark and Doppler components can dominate the emission spectra and obscure the Zeeman component. In this research, we are developing a time-resolved multi-axial technique for measuring the Zeeman, Stark, and Doppler broadened line emission of dense magnetized plasmas for Z-pinch and Dense Plasma Focus (DPF) accelerators...
November 2016: Review of Scientific Instruments
Zaisheng Lin, He Wang, Xiang Peng, Teng Wu, Hong Guo
We report a laser-pumped (4)He atomic magnetometer with light shift suppression through the atomic sensor itself. A linearly polarized light is used to optically align the (4)He metastable atoms and we monitor the magneto-optical double resonance (MODR) signals produced by the left- and right-circularly orthogonal components. It is shown that light shift leads to the atomic alignment to orientation conversion effect, and thus, the difference between the two MODR signals. One of these two MODR signals is locked at the Larmor frequency and is used to measure the ambient magnetic field, while the differential signal is, simultaneously, fed back to suppress the light shift...
November 2016: Review of Scientific Instruments
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